Regional climate models predict an intensification of extreme heat waves in Central Europe. Against this background, the significance of human-biometeorologically orientated urban planning strategies is increasing by which the impairment of thermal comfort for people in cities in the future can be minimised. Such strategies require quantitative information on factors determining human thermal comfort within different urban quarters. With respect to these problems, the joint research project KLIMES funded by the German Federal Ministry of Education and Research was initiated. Its methodical approaches and objectives are presented in this article. One part of KLIMES are experimental investigations on human thermal comfort within different urban street canyons, whose variable arrangement generally characterises urban quarters. The investigations are conducted in Freiburg (SW Germany). The experimental design and the concept to analyse the measured data related to the objectives of KLIMES are exemplarily explained based on investigations in the Rieselfeld quarter on a typical summer day in 2007. The internationally well-known physiologically equivalent temperature PET is used as thermal index to quantify the perception of the thermal conditions by a collective of people within cities. During typical summer weather in Central Europe, PET is strongly influenced by the radiation heat, which is parameterised by the mean radiant temperature T mrt. Therefore, the short- and long-wave radiation flux densities from the three-dimensional surroundings of a standardised standing person representing mean properties of a collective of people in cities are analysed in detail. For the specific conditions at the stationary site Rieselfeld (NW-SE oriented urban street canyon, H/W = 0.49, SVF = 0.51, SW oriented sidewalk), the contribution of the total long-wave radiation flux density absorbed by a standing person to T mrt increased during the day from about 70% in the morning to about 90% in the evening before sunset.
Abstract in Undetermined This study deals with a current problem of urban human-biometeorology on the micro-scale, which becomes more important due to the future increase of severe summer heat in Central Europe. The impact of street design parameters on the thermal comfort of citizens is analysed in an experimental way for typical summer conditions in Central Europe. The investigation is focused on the behaviour of mean radiant temperature Tmrt and physiologically equivalent temperature PET as the most important human-biometeorological variables for thermal comfort during these atmospheric conditions. To get quantitative results on how they depend on small-scale characteristics of urban street canyons, an investigation design is applied which is based on measurements of relevant meteorological variables - like air temperature Ta - by specific humanbiometeorological measuring systems. They were conducted in selected street canyons within different urban quarters of Freiburg, the warmest city in Germany, from 2007-2009. Tmrt and PET were calculated from the measured meteorological variables by well-tested approaches. The geometry of urban street canyons is characterised by (i) the sky view factor SVF determined from fish-eye photos, (ii) the ratio of building height H to street width W, (iii) the orientation to the sun, and (iv) the fraction of ctc (coverage by the street tree canopy). To eliminate the influence of slightly different weather conditions even on typical summer days, the results are not presented in form of absolute values for the human-biometeorological variables, but in form of ratios for the measured radiative flux densities and in form of differences for the measured and calculated temperatures. As the results for Tmrt and PET should primarily quantify universal patterns of the impact of street design parameters on human thermal comfort, they are only presented as mean values for the period 10-16 CET. The main results obtained from different analyses are: (i) SVF for the southern half of the upper hemisphere (SVF90-270) is more suitable to characterise the sites with respect to the thermal perception of citizens than SVF for the whole upper hemisphere (SVF1-360), (ii) in contrast to wide E-W oriented street canyons, narrow E-W oriented street canyons have larger spatial differences in Ta, Tmrt and PET, (iii) with respect to the orientation, these differences are larger in E-W than in N-S oriented street canyons, and (iv) an increase of ctc by 10 % leads to a decrease of Ta by only 0.2 °C, but to a reduction of Tmrt by 3.6 °C and of PET by 1.4 °C. (Less)
